Conventional personal computers (also called PC-based automation systems) are increasingly being used in the automation of power plants instead of conventional stored program control (called SPC for short). The conventional stored program control has fixed wiring irrespective of the respective control task which is adapted by a program to the plant to be controlled. In contrast hereto there exist as an alternative stored program control hardwired program controls which, however, have to be converted in terms of hardware in the event of a change to the control sequence.
Modern PC-based automation systems comprise automation devices, constructed as personal computers, with basic software. PC-based automation systems of this kind are becoming increasingly more important owing to the simple creation of system and user software based on modern programming languages. The basic software generally comprises a real-time operating system and specific programming modules (also called “modular units”) which simulate automation functions such as open-loop control, closed-loop control, AND/OR functions, adders and other logic elements. A communication program to allow a plurality of automation devices to communicate with each other and/or with external data processing units, such as with a programming device, is conventionally also provided. A PC-based automation device operates like a conventional stored program control according to what is known as the IPO principle (IPO=input, processing, output).
The drawback of a PC-based automation system lies in inadequate availability. While SPC-based automation systems allow, for example, smooth changeover in the millisecond range, according to predefinable availability requirements, with a PC-based automation system this lies in the second range owing to monitoring by means of what is known as a watchdog function. Recognition of a fault and a resulting changeover from a faulty automation device to a faultless automation device is subject to predefined safety requirements and the reliability of the automation system for process management and process monitoring of the plant. In order to also be able to use a PC-based automation system for safety-relevant systems in a power plant, fast and reliable fault recognition and, resulting therefrom, an optimally smooth changeover are required during operation.